Add LCStore implementation that uses static arrays in PHP files

Add LCStore implementation that uses static arrays in PHP files

Implementation written by Fred Emmott of Facebook. Quoting Fred:

As well as array access being faster, the main advantage is actually
that this significantly reduces the use of unserialize(), which does a
lot of memcpys when making the strings.

Benchmarks compared to LCStoreCDB:
* HHVM (no repo-auth): ~7% improvement
* HHVM (with repo-auth): ~12% improvement
* PHP7: ~1% improvement

My (Legoktm) brief testing noted that the generated PHP files were
noticiably larger than the CDB ones:
* 1.5M	en.l10n.php
* 932K	l10n_cache-en.cdb

Bug: T99740
Change-Id: Ib2c5856d40cd928cab4a79cb935b3ce08c598300